Howdy all.
Just a general status update regarding our plasma cutter water table and the anti rust chemicals that I use in it.
Since we have set up our cnc plasma cutter, it has been a full year now. In that period of time, we have done a lot of cutting.
First observation and opinion.. I totally love our water table. There is absolutely NO way that I would ever accept a dry cutter now. The water absorbs virtually all the smoke and dust that the plasma cutter produces, and allows us to cut in the shop, without having to worry about a dedicated ventilation system for the plasma machine. That saves us having to heat make up air in the winter.
Having the water table also makes it very nice in removing cut parts. Even though we normally set the water level at just under the bottom surface of the metal, the splash up of the water, from the plasma air jet instantly cools the part, which allows it to be picked up by hand immediately. This instant cooling also tends to greatly reduce warping of thin section parts, particularly of stainless steel, due to the heat of cutting.
After a year of cutting, we have not changed the water until just the other day. We finally drained the system and removed the cutting grates to allow us to muck out the bottom of the table. There was approximately 1 inch of "mud" in the bottom of the table, which consisted mostly of fine metal dust. I believe that some "smoke" compounds were a component of the "mud" as well, as we cut lots of material with vinyl protective "laserguard" film on it. Once the grates were lifted out of the way, and the water level drained to its lowest, it was a simple matter to shovel out the "mud" into buckets for disposal.
Second observation and opinion, regarding anti rust chemicals.
Our water table is made from 304 stainless steel, but the cutting slats I constructed of 14 gauge carbon steel... cold rolled mostly. At the initial filling of the table with water, I added approximately 4 pounds of sodium nitrite and 3 pounds of 20 mule team borax to the 190 gallons of water that our table/reservoir holds.
In that year, there has been NO observable rusting of any of the carbon steel slats or any of the cutting drops that were found in the bottom of the table at mucking out. The steel slats have been exposed to water levels that normally left the top 1/8 inch or so above water level, and the rest submerged, with periods of a day or so where I had the water level down lower, exposing most of the slats to air. It is my opinion that the sodium nitrite and borax did a very fine job of preventing corrosion of the metals exposed to the table water.
One thing I do note though is that when galvanized steel is exposed to the treated water for an extended period of time, it WILL be affected by the chemicals involved, or possibly a galvanic reaction with the chemically treated water as an electrolyte. I added a few galvanized cutting slats and found that they reacted strongly with the water and perhaps the stainless steel table.
When cutting galvanized, I simply make the cuts and then remove the cut parts in a more or less timely manner from the table and dry them off, and there are no adverse reactions.
We use a Hypertherm 1250 plasma cutter with a machine torch, and I could not be happier with it. Normally I used fine cut consumables since we cut mostly 3/16s or less in thickness, either carbon steel or stainless steel. While I normally run the torch above water level, I have at times cut with the torch tip fully submerged and that seems to work fine as well. I dont leave the torch standing in water, since water would tend to infiltrate into the torch tip and around the electrode, which is not a good idea. Though its a probably a point for another thread, I have made a simple modification to our hypertherm plasma cutter, which allows it to have a slow trickle of air at low pressure into the torch, even when the torch is off. This keeps the water out of the torch when it is not cutting but the tip is submerged, with a slow bubbling of air from the torch tip, but I cut with the tip submerged so infrequently that I normally dont turn this feature on. If I ever set our machine up to cut on nitrogen and fully submerged for stainless steel, I will begin using this trickle flow on a regular basis.
Sorry for the long post, but it might be of use to someone out there.
Best Wishes and happy cutting!